1. Field of the Invention
The invention relates to the field of power generation systems for use on spacecraft and/or on other heavenly bodies with little or no atmosphere (e.g., on the moon). More particularly, the invention concerns a power generation system which extracts power using a Rankine cycle engine having a refrigerant circulating between a relatively hotter area exposed to solar radiation and a relatively cooler area shaded from solar radiation.
2. Prior Art
Vehicles operating in outer space require mechanical and/or electrical power for various operating systems such as communications, guidance, computers, artificial environment, etc. This power must be generated on board. Several different sources of power generation have been utilized on space vehicles, either alone or in combination. Solar power electrical systems, for example, utilize large panels having photovoltaic cells for converting solar energy to electrical power. Nuclear power systems have been utilized which use nuclear fuels to generate power in a small scale nuclear reactor. Also, fuel cells which combine hydrogen and oxygen to provide electrical power have been employed. Such fuel cells are utilized extensively on the space shuttle. Additionally, magnetohydrodynamic power generation systems for space based vehicles have been proposed and are under development.
Spacecraft power generation systems have some unique requirements due to the need to conserve weight and volume in the spacecraft, and due to the fact that the spacecraft is isolated by the vacuum of space. With reference to these unique aspects of spacecraft, prior art power generation systems have been characterized by certain shortcomings in equipment size, weight, and efficiency. For example, photovoltaic solar panels typically yield efficiencies only in the thirty percent to fifty percent range, and thus require extremely large surface areas for generation of any substantial portion of the spacecraft's power requirements. It is difficult to transport large solar panels into outer space, particularly if a number of panels are required, and it is also difficult to deploy them. Solar panels are easily damaged by space debris. Further, solar panels are undesirable for secret space systems because their large size and vulnerability to damage make them easy targets.
Consequently, for space vehicles requiring relatively large amounts of power, the prior art has resorted to fuel cells or nuclear generators. The fuel cells and nuclear generators are heavy and bulky since they effectively carry their power source in a self contained manner. The weight of such power generation apparatus decreases the weight of potential payloads and takes up valuable cargo space. Nuclear reactor fuel systems require heavy shielding and also are dangerous because an aborted launch or a problem with attaining and/or maintaining orbit can result in dangerous and virtually irreparable contamination of the earth or sea.
Whereas the size and weight of power generation systems are very important for spacecraft applications, the efficiency of such systems is important. A more efficient smaller and/or lighter system which can provide the same power as a larger or heavier one is of course desirable. All power generation systems are typically less than one hundred percent (100%) efficient, and the fuel cells which are currently used to provide electrical power for the space shuttle are only forty percent (40%) to a potential maximum of approximately seventy percent (70%) efficient in extracting the power available from their self-contained fuel supplies.
There is a need for a reliable power generation system for use on spacecraft which is smaller, lighter and more efficient than the prior art power generation systems. Further, there is a need for a space based power generation system of this type which obtains energy from outside sources and does not require storage or replenishment of fuel. Similar needs apply for power generation systems which can be sent to and employed at a base on the moon or other heavenly body with little or no atmosphere to support convective cooling. The present invention provides these and other advantages by utilizing naturally occurring temperature differences between areas exposed to solar radiation and areas shaded from solar radiation.